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Biomedical subjects

E Henneman

Publications and source records attributed to E Henneman.

At least 37 records · Page 2Linked to original sources
PubMed1979

Different species of alpha motoneurons in same pool: further evidence from effects of inhibition on their firing rates.

1. Single units of the plantaris pool were isolated in ventral root filaments of decerebrate cats and their critical firing levels (CFLs) were determined. Motoneurons of similar size were compared in firing rate (FR) during repetitive stimulation of the plantaris nerve to establish control values and also during added stimulation of various inhibitory nerves (sural, hamstrings, or peroneal). 2. Criteria, based on maximal firing rate, were developed whereby certain pairs of units of similar size could be reliably classified into different types. 3. A second, independent set of criteria was formulated by which the same pair of units could be classified according to their responses to added inhibitory inputs. 4. The ability to distinguish motoneurons consistently by more than one set of criteria reinforces the evidence that different physiological types of units exist within a single motoneuron pool. 5. The findings indicate that different types of cells either receive different densities of input from certain inhibitory sources or that they react differentially to the same amounts of these inputs.

Action Potentials↗
PubMed1977

Identification of two species of alpha motoneurons in cat's plantaris pool.

1. Single units of the plantaris pool were isolated in ventral root filaments of decerebrate cats and their critical firing levels (CFLs) were determined. Motoneurons of similar size, as judged by their CFLs and other criteria, were compared in firing rate (FR) during repetitive stimulation of the plantaris nerve. 2. Such units either differed very little or quite widely, suggesting that they were sampled randomly from two populations, one firing rapidly, the other slowly. The relationship between the two rates remained approximately constant, regardless of the intensity or rate of input the units received, as long as both of them discharged rhythmically. 3. In single experiments 10-15 of the smallest units in the pool (all with CFLs in the 0-8% range) were isolated and compared. Statistical analyses and visual inspection of these small samples again suggested the existence of two species of motoneurons. 4. Statistical analyses also indicated that the FRs of units in single experiments were not sampled from any one of a variety of parametric, single-modal distributions. This suggests that the data were sampled from a distribution having more than one mode, indicating the existence of separate populations or species of motoneurons among the small units of the pool (0-8% range of CFL). 5. Pooling of the normalized data from different experiments revealed a bimodal histogram, reinforcing the conclusion that there are two species of small alpha motoneurons in the plantaris pool.

Animals↗
PubMed1976

Electrical measurement of axon diameter and its use in relating motoneuron size to critical firing level.

1. Action potentials of single plantaris motoneurons were recorded monophasically from fine ventral root filaments. A resistor was placed in shunt across the recording electrodes and its value was varied until the size of the action potentials was reduced by one-half. At this point the resistance of the filament was taken to be equal to that of the shunt, and the quotient of action-potential amplitude divided by filament resistance was proportional to the axonal action current. 2. The measurement of axonal action currents depends on the assumption that the filament-electrode system obeys Ohm's law. Tests were performed which validated this assumption. It was then shown that the axonal action currents varied as the square of conduction velocity over the range of alpha and gamma motoneurons. 3. A direct correlation was established between the critical firing levels of motoneurons and the sizes of the impulses in their axons after the recorded sizes had been normalized in accordance with the resistances of the ventral root filaments in which they were located. Since both the CFL and axonal diameter were related to impulse size, they were related to each other (Fig. 6). 4. Evidence is cited justifying the conclusion that the dimater of a motor axon is directly related to the size of its soma. Thus, it may be inferred that the critical firing level of a motoneuron is a function of its size.

Action Potentials↗
PubMed1968

Terminals of single Ia fibers: distribution within a pool of 300 homonymous motor neurons.

The excitatory postsynaptic potentials produced in motoneurons by impulses in single afferent fibers (Ia) have been recorded with the aid of an averaging computer. These responses were used to map the distribution of the terminals of single fibers within the pool of 300 motoneurons of the medial gastrocnemius muscle. Twelve Ia fibers were studied in separate experiments. Monosynaptic excitatory postsynaptic potentials were found in 94 percent of the 77 motoneurons investigated. This finding indicates that each of the 300 motoneurons must receive afferent fibers from almost all of the spindles of the muscle it innervates.

Animals↗